Selection Pressures

Some species of insects have changed very little over millions of years.

• Disruptive

• Directional

• Stabilising

Elephants have evolved longer trunks enabling them to reach leaves higher up in trees.

• Disruptive

• Directional

• Stabilising

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Small individuals of a mammal species can escape from predators by hiding in small spaces whilst large ones can resist attack by predators.

• Disruptive

• Directional

• Stabilising

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The most important type of selection in bringing about evolutionary change.

• Disruptive

• Directional

• Stabilising

The mean ear length in Artic foxes has reduced over time.

• Disruptive

• Directional

• Stabilising

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It preserves the characteristics of a population.

• Disruptive

• Directional

• Stabilising

Long wiggly tails in lizards look like snakes to scare off predators.

• Disruptive

• Directional

• Stabilising

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Short tails mess up a leopard’s balance; long tails drag on the ground - medium tails are best.

• Disruptive

• Directional

• Stabilising

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Short tails help a squirrel escape predators on the ground; long tails help with balance in trees - medium tails are no good.

• Disruptive

• Directional

• Stabilising

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A forest floor is a fairly consistent shade of brown. Mice whose fur is most-closely matched to that colour will probably survive. Mice that are slightly lighter or slightly darker will stand out against the ground.

• Disruptive

• Directional

• Stabilising

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